In most ink jet printers, piezoelectric and similar print heads eject ink onto print documents or substrates. Some print heads eject UV-curable gelated inks, or similar inks that have a high viscosity at room temperature and a low viscosity when heated. The print heads heat the ink until the ink is liquid, and fire the ink droplets from the print head onto a document or other substrate, such as plain or coated paper. Once the ejected ink contacts the substrate, the ink changes from the low viscosity liquid back to a more viscous consistency. However, there can be a period of time when the ink is substantially liquid and can flow into the fibers of the substrate. Several factors related to the substrate can affect how much ink flows into the substrate fibers such as, for example, pore size, formation index, basis weight, and other factors. If the ink penetration is severe enough, ink can be seen from the back side of the substrate, a condition known as show-through. When a substrate has too much show-through, the substrate can be unacceptable for duplex printing.
Various systems and methods exist that attempt to minimize the show-through condition. For example, cooling the substrate at the time of printing can arrest the flow of ink. However, cooling can use a lot of energy and can create other down-stream issues. Further, depending on the type of substrate used, mitigation of show-through may not be needed because show-through may not be an issue, and therefore cooling the substrate would be a waste of energy.
Various systems and methods also exist that attempt to measure the amount of show-through on a substrate. For example, a densitometer can measure the degree of darkness of a material, and in particular the back (non-printed) side of a substrate. In particular, the densitometer is a light source that can be aimed at a photoelectric cell, and can determine the density of a sample placed between the light source and the photoelectric cell. However, the densitometer measurements are inherently limited due to the size of the aperture of the densitometer. As such, the densitometer is not a device that is well-suited to capture variation in show-through because elements such as paper formation differences can be larger in scale and/or location than the aperture.
A need, therefore, exists for systems and methods to effectively and efficiently calculate and measure the amount of show-through on a printed document. In particular, a need exists for systems and methods whereby the amount of show-through of a document can be given a quantitative value that can be later used to modify parameters to improve performance without using excessive amounts of energy, while simultaneously increasing yield.